1. Field of the Invention
The field of the invention relates to a boxspring having means for limiting the compression of at least some of its coil springs to prevent coil setting.
2. Brief Description of the Prior Art
Boxsprings used for supporting mattresses have typically included a plurality of conical, hourglass or uniform diameter coil springs of equal height stapled or otherwise secured to a wood, plastic or steel frame. Such a construction is shown in commonly assigned U.S. Pat. No. 4,399,573 in the name of Leslie I. Baright. The boxspring disclosed in this prior application provides a pair of braces for support of the frame.
It is well known that certain portions of a boxspring are subject to disproportionate loads during use. Whereas a person is usually in a reclining position near the central portions of a bed, thereby distributing the load relatively evenly, the ends and sides of the bed are often used for sitting, thereby providing a greater force over a smaller area. The problems are often particularly acute in hotels and motels where a number of persons may use the bed as a sofa in the absence of adequate seating.
The boxspring supporting the mattress can become damaged when the bed is used too often as a seating structure. If the coil springs are compressed beyond a certain point, they will become "set" and will not recover their original height. This is due to the fact that the springs are designed to have limited deflection ability. Once the boxspring is damaged in this manner, the entire bed may appear tilted and sleeping comfort will be substantially impaired.
The spring designer is faced with a dilemma in attempting to overcome the above problems. A spring construction which allows full compression (convolutions touching) is too soft to meet the needs of the marketplace. A firmer boxspring requires the coil design to allow only partial compression before set (overstress) occurs. Most boxspring coils used today will not recover their original height when compressed more than half of this height.